Compressed-air arrangement for trucks

ABSTRACT

A compressed-air supply system for goods vehicles, comprising an air-suspension system and a brake system, wherein the brake system is dimensioned to operate at a lower air pressure than the air-suspension system, and wherein the compressed-air supply system comprises at least one compressed-air tank (43, 51) for supplying the brake system with compressed air. The compressed-air tank (43, 44) is dimensioned for an air pressure which is greater than or equal to the air pressure which is demanded in the air-suspension system and, further, the compressed-air tank is connected to both the air-suspension system and the brake system and comprises compressed-air conduits (40, 40&#39;; 52, 52&#39;) through which compressed air can pass by way of one or more outlets in the compressed-air tank (43, 51) to the brake system and the air-suspension system, respectively, wherein a pressure-limiting valve (44, 55) is arranged downstream of the outlet to the compressed-air conduit(s) connecting the compressed-air tank (43, 51) with the brake system.

TECHNICAL FIELD

The invention regards a compressed-air supply system for truckscomprising an air-suspension system and a brake system, wherein thebrake system is dimensioned to operate at a lower air pressure than theair-suspension system, and wherein the compressed-air supply systemcomprises at least one compressed-air tank for supplying the brakesystem with compressed air.

BACKGROUND

When a truck is provided with air-suspension, it is necessary that thecompressed-air supply system of the vehicle has sufficient capacity toallow quick and efficient loading and unloading cycles. Large amounts ofcompressed air are consumed, particularly when connecting anddisconnecting swap bodies and so called trailers, or semi-trailers.However, at the same time the compressed-air system must primarily havesufficient capacity to meet the demand of compressed air for thevehicle's brake system.

Trucks having air-suspension are usually provided with special highpressure compressors and with high pressure tanks for the air-suspensionsystem containing up to 110 liters of air. The air-suspension system issupplied with compressed air at an air pressure of between 7 bar up to12 bar. The brake system operates at a considerably lower air pressure,between 5 bar and 7.5 bar. For this reason, the vehicle must be providedwith separate air supply systems and separate compressed-air tanks forthe brakes and the air-suspension. Furthermore, the vehicle's brakesystem comprises special compressed-air tanks for the front and the rearbrake circuit, respectively. Taken together, this implies thatconventional trucks with air-suspension usually have about eight airtanks which must be built into the chassis of the vehicle. In order toachieve this, a very complicated and expensive design of the chassis isrequired, since, of course, the available space is limited.

Moreover, the many air tanks require that space, which otherwise couldbe used for transporting goods, must be reserved for storage ofcompressed air. In addition, the weight of the air tanks detracts fromthe weight of the goods which may be transported by the vehicle.

However, with the present invention a compressed-air system of the typementioned in the introduction has been achieved, offering thepossibility of reducing the number of compressed-air tanks.

The compressed-air system in accordance with the invention is primarilydistinguished by the compressed-air tank being dimensioned for an airpressure which is greater than or equal to the air pressure which isdemanded in the air-suspension system and further by the compressed-airtank being connected to both the air-suspension system and the brakesystem and comprising compressed-air conduits through which compressedair can pass by way of one or more outlets in the compressed-air tank tothe brake system and the air-suspension system, respectively, wherein apressure-limiting valve is arranged downstream of the outlet to thecompressed-air conduit(s) connecting the compressed-air tank with thebrake system.

By using a compressed-air system in accordance with the invention, it ispossible to largely utilize the same air tanks for the air supply to thebrake system as for the air-suspension. Hereby, the number ofcompressed-air tanks which is required to supply a vehicle withcompressed air may be reduced by one or several tanks. By storingcompressed air at a pressure of 12 bar in the brake air tanks, the aircan be used in the upper pressure region for the air-suspension and inthe lower pressure region for the brake system.

This is preferably achieved by the use of a seven-port protection valvehaving four compressed-air circuits. Further, pressure limiting valvesare employed in order to obtain a lower pressure in the respective frontand rear brake circuits of the vehicle.

For certain types of goods vehicles having a rear overhang, it ispossible to omit the compressed-air tank which, when using aconventional compressed-air supply system, is placed in the overhang.Hereby, it is also possible to omit the cross-bar on which thecompressed-air tank is mounted, whereby the overhang can be shortened.This results in a saving of both weight and space.

SHORT DESCRIPTION OF DRAWINGS

In the following, the invention will be described in more detail, withreference to the appended drawings.

In the drawings:

FIG. 1 shows a schematic view of a conventional compressed-air supplysystem;

FIG. 2 shows a schematic view of a compressed-air supply system inaccordance with the invention;

FIG. 3 shows a truck with compressed-air tanks; and

FIG. 4 shows a different type of truck with compressed-air tanks.

DETAILED DESCRIPTION OF THE INVENTION

The conventional compressed-air system which is shown in FIG. 1comprises a four-circuit protection valve 1 having five ports 2-6. Theprotection valve 1 comprises four overflow valves 7-10 and twonon-return valves 11,12.

A compressor 13 delivers air at a pressure of 12 bar. The air is passedthrough an air dryer 14 and into a distribution tank 15 which is a wettank, dimensioned for a pressure of 12 bar. Two air conduits 16,17, anair-suspension air conduit 16 to the air-suspension system (not shown inthe drawing), and a brake air conduit 17 to the brake system via theprotection valve 1, run from the distribution tank 15. The air conduit16 to the air-suspension system passes a first overflow valve 18 whichonly opens for air passage into the system if the air pressure exceeds6.7-7.0 bar. If the air pressure after the first overflow valve 18exceeds 10.0-10.4 bar, a second overflow valve 19 is opened into anair-suspension tank 20, which thereby is filled with air. Otherwise, thecompressed air is conducted out through the air-suspension air conduit16 to the air-suspension system.

The air to the brake system is conducted in the brake air conduit 17through a pressure-limiting valve 21. The air flow is thereafter furtherconducted through the first port 2 in the five-port protection valve 1and is divided up into two conduits 22,23 one for the rear brake circuitand one for the front brake circuit. Back-flow through the two conduits22,23 is limited by two further overflow valves 7,8 which are arrangedon each air conduit 22,23 as components of the protection valve 1. Afterthe overflow valves 7,8, each air flow is divided again so that oneportion is conducted out to a rear and a front brake tank 24,25,respectively, and one part of each air flow is conducted through anon-return valve 11,12 to a parking air tank 26 and to an outlet foradditional equipment 27. Backflow from the parking air tank 26 and theoutlet for additional equipment 27 is limited by a fourth and a fifthpressure-limiting valve 9,19 which allow back-flow of air at a pressureexceeding 5.5-5.8 bar.

The compressed-air tanks which are shown in FIG. 1 as supplying theair-suspension system and the front and rear brake circuits withcompressed air have, for the sake of simplicity, each been shown as asingle tank. In reality, both the air-suspension tank 20 and the braketanks 24,25 usually consist of two or more compressed-air tanks each.

As is realised by studying the previously known air supply system shownin FIG. 1, this system is designed to primarily supply the brake systemwith compressed air and secondly the air-suspension system. Since theair pressure in the brake circuits is considerably lower than thepressure in the air-suspension system, separate compressed-air tanks areneeded for the two systems.

An air supply system in accordance with the invention, as shown in FIG.2, comprises a compressor 30 which delivers air at an air pressure of12.5-13.0 bar through an air dryer 31 to a distribution tank 32. Afterthe distribution tank 32 the compressed air is divided into two airconduits 33,34 whereby an air-suspension air conduit 33 leads to thevehicle's air-suspension system and a brake air conduit 34 leads to thevehicle's brake system. The compressed air passes into theair-suspension system through an overflow valve 35 which is opened at6.7-7.0 bar and which does not allow back-flow. The compressed air isthereafter collected in an air-suspension tank 36 after passage throughan overflow valve 37 which is opened at 10.0-10.4 bar and which allowsfull back-flow. The air-suspension tank 36 supplies the air-suspensionsystem with compressed air via the air-suspension air conduit 33.

The compressed air is conducted through the brake air conduit 34 fromthe distribution tank 32 to the brake system in through a first port 38on the high pressure side of a seven-port four-circuit protection valve39. In the protection valve 39, the compressed-air flow is furtherdivided into two parts which supply the rear brake circuit and the frontbrake circuit of the vehicle, respectively.

In the rear brake circuit, the compressed air is passed through a rearbrake conduit 40 through a first pressure-limiting valve 41 which ispart of the protection valve 39 and which allows back-flow at a pressureexceeding approximately 5.0 bar. The compressed air is thereafter passedout through a second port 42 on the high pressure side of the protectionvalve 39 to a rear brake circuit air tank 43. By arranging apressure-limiting valve 44 downstream of the outlet in the air tank 43of the rear brake circuit, the compressed air obtains a lower airpressure which is adapted to the brake system.

The air tank 43 of the rear brake circuit is connected to a foot-brakevalve 45. Further, the air is conducted in a brake circuit conduit 40'from the air tank 43 to the low pressure side of the protection valve 39through a fourth port 46 in the protection valve 39 and out through asixth port 47 to a parking air tank 48. Furthermore, via the fourth port46, the air tank 43 of the rear brake circuit is connected to an outletfor additional equipment in communication with a seventh port 49 in theprotection valve 39.

In a corresponding manner as for the rear brake circuit, thecompressed-air tank 51 of the front brake circuit is supplied withcompressed air through a front brake air conduit 52 and via a secondoverflow valve 53 which allows back-flow at a pressure exceedingapproximately 5.0 bar. The air is passed from the high pressure side ofthe protection valve 39 to the air tank 51 through a third port 54 inthe protection valve 39. In order to obtain a suitable air pressure forthe brake system, as in the rear brake system, the air is conducted fromthe air tank 51 of the front brake circuit through a pressure-limitingvalve 55. After the pressure-limiting valve 55, the air tank 51 of thefront brake circuit is connected to the parking brake air tank 48 andthe outlet for additional equipment 50 via a brake air conduit 52' and afifth port 56 in the protection valve 39. In addition, the air tank 51of the front brake circuit is also connected to the foot-brake valve 45.

The air supply to the parking air tank and the additional equipmentthrough the sixth port 47 and the seventh port 49 in the protectionvalve 39 is controlled by an overflow valve 57,58 which is connected toeach of the ports 47,49. The overflow valves 57,58 are opened at apressure of 5.5-5.8 bar and allow limited back-flow to a connectingconduit 59 between the two ports 47,49. In order to prevent thecompressed air from flowing back out of the protection valve 39, anon-return valve 60,61 is arranged inside each of the fourth and thefifth ports 46,56 in the protection valve 39.

In the same way as for the compressed-air system shown in FIG. 1, thecompressed-air tanks shown in FIG. 2 may each consist of two or moretanks. However, taken as a whole, the compressed-air system shown inFIG. 2, in accordance with the invention, requires fewer compressed-airtanks than the conventional compressed-air system shown in FIG. 1, sincethe same compressed-air tanks to a large extent may be utilized forstoring air both for the air-suspension system and for the brake system.In a conventional compressed-air system, the air-suspension tank isoften a tank which holds 50 liters and two tanks of 30 liters each.However, in some vehicles only a tank of 50 liters or a tank of 50liters and a tank of 30 liters is used. The compressed-air tank of therear brake circuit usually consists of one or two tanks holding 30liters and the compressed-air tanks of the front brake circuit normallyhold 30 liters. The invention makes it possible to utilize thecompressed air in the brake circuits to completely or partially supplyalso the air-suspension system with compressed air. Since thecompressed-air tanks of the brake circuits hold at least 60 liters ofcompressed air, these tanks can always take the place of the 50 litertank which is used for the air-suspension in conventional systems. Invehicles having brake circuits which together contain 90 liters, thecompressed-air tank volume for the air-suspension may be reduced by afurther 30 liter tank. The number of tanks which may be eliminateddepends on whether the vehicle has two or three axles, since a vehiclewith three axles has more brake air tanks than a vehicle with two axles.

By eliminating one or more compressed-air tanks, the weight of thevehicle is reduced by at least 50-60 kg which implies that the loadingspace and the loading weight are increased. The weight reduction ispartly due to the fact that fewer air tanks are used but also to thereduced demand for other components such as consoles, pipes and nipples.

FIG. 3 shows how compressed-air tanks comprised in a conventionalcompressed-air system are placed on the chassis 69 of a goods vehicle.Thereby, the chassis 69 exhibits a distribution tank 70 and threecompressed-air tanks 71,72,73 which are part of the air-suspensionsystem. In addition, a compressed-air tank 74 supplies the front brakecircuit with compressed air and two compressed-air tanks 75,76 supplythe rear brake circuit. Moreover, a parking air tank 77 is applied tothe chassis 69.

The number of compressed-air tanks may be reduced, in accordance withthe invention, by eliminating the compressed-air tanks 71,72,73 to theextent that a corresponding volume is available in the compressed-airtanks 74,75,76 belonging to the brake circuits. Accordingly, the rearcompressed-air tank 71 for the air-suspension system as well as one ofthe brake air tanks 74,75,76 arranged centrally on the chassis 69 may beeliminated in accordance with the invention, since the compressed air inthe brake air tanks 74,75,76 has a sufficiently high pressure to be usedalso in the air-suspension system.

FIG. 4 shows a part of a chassis 80 of a conventional goods vehiclewherein the vehicle chassis 80 has a rear overhang 81, onto which ismounted an air tank 82 belonging to the brake system and an air tank 83for the air-suspension system. Furthermore, the chassis 80 exhibits anadditional brake air tank 84, a distribution tank 85, and a parking airtank 86. In a vehicle which is provided with a compressed-air system inaccordance with the invention, the air tank 83 belonging to theair-suspension system may be eliminated. This is an advantage forseveral reasons. In this manner, it is possible to shorten the overhang81 and to remove the transverse beam 87 on which the air tank 83 ismounted. Consequently, the weight of the vehicle is reduced and theloading capacity is increased both by the elimination of the air tank 83and by making the overhang 81 smaller.

The invention shall not be regarded as being limited by the hereindescribed embodiments. Accordingly, a number of further variants andmodifications are conceivable within the scope of the appended claims.

What is claimed is:
 1. A compressed-air system for goods vehicles,comprising an air-suspension system and a brake system, wherein thebrake system is dimensioned to operate at a lower air pressure than theair-suspension system, and wherein the compressed-air supply systemcomprises at least one compressed-air tank for supplying the brakesystem with compressed air wherein the compressed-air tank isdimensioned for an air pressure which is greater than or equal to theair pressure which is demanded in the air-suspension system and furtherthat the compressed-air tank is connected to both the air-suspensionsystem and the brake system and comprises compressed-air conduitsthrough which compressed air can pass by way of one or more outlets inthe compressed-air tank to the brake system and the air-suspensionsystem, respectively, wherein a pressure-limiting valve is arrangeddownstream of the outlet to the compressed-air conduit(s) connecting thecompressed-air tank with the brake system.
 2. A compressed-air supplysystem in accordance with claim 1, wherein the brake system comprises afront and a rear brake circuit which are supplied with compressed airfrom at least one compressed-air tank, and that the compressed-airsupply system comprises a four-circuit protection valve having sevenports, wherein the protection valve exhibits a high pressure side and alow pressure side and that conduits for compressed air are arrangedthrough the high pressure side of the protection valve in to thecompressed-air tank and that conduits are arranged from thecompressed-air tank to both of the brake circuits via the low pressureside of the protection valve wherein each such conduit to the brakesystem exhibits a pressure-limiting valve which is arranged between thecompressed-air tank and the protection valve (39).
 3. A compressed-airsupply system in accordance with claim 2, wherein both of the brakecircuits are supplied with compressed air from separate compressed-airtanks.
 4. A compressed-air supply system in accordance with claim 1,wherein the pressure difference between the air-suspension system andthe brake system is at least 2.5 bar.
 5. A compressed-air supply systemin accordance with claim 4, wherein the pressure difference between theair-suspension system and the brake system is at least 1.5 bar.
 6. Acompressed-air supply system in accordance with claim 1, wherein theair-suspension system operates at an air pressure of between 7 and 12bar, and that the brake system operates at an air pressure between 5 barand 7.5 bar.
 7. A compressed-air supply system in accordance with claim5, wherein the air-suspension system operates at an air pressure ofbetween 10 bar and 12 bar and that the brake system operates at an airpressure between 6 bar and 7 bar.